Still, Rouhani faces serious challenges from two powerful conservative contenders, including Ebrahim Raisi, a close ally of the Supreme Leader Ayatollah Ali Khamenei.

He has been described by AFP as a hard-line judge and cleric who has little political experience but is well connected to Iran's ruling establishment.

Raisi has been tipped to be a future supreme leader, the most powerful position in the land. Like Ahmadinejad in the past, he has positioned himself as modest public servant and supporter of the poor during these tough economic times.

Initial excitement surrounding Rouhani - who was instrumental to a nuclear deal with the West - has died down, with some economic sanctions remaining in place while a stagnant economy sees some of the country's poorest suffer.

Another conservative challenger looking at challenging the status quo is Tehran mayor and former Republican Guard commander Mohammed Bagher Ghalibaf, who has been described as "a hard-liner".

Rouhani faces a struggle against these two strong, populist contenders, experts say, during a time of economic and political uncertainty.

His relatively open political outlook and liberal economic vision is at odds with the conservatives who are looking to side-line moderates and provide subsidies for the poor and a closed economic model.

Meanwhile, the election of Donald Trump could empower conservatives further as the new US administration pushes for a tougher line against Iran that has threatened to tear up the nuclear accord.

Experts say the conservative-dominated establishment in Iran are looking to encourage voters to turn out and back hard-line candidates. The absence of any televised debates this year could put off some younger voters who might otherwise back Rouhani.

"They [government] need that for legitimacy - the turnout is even more important than the result," Clement Therme, research fellow for Iran at the International Institute for Strategic Studies told AFP.

Elections are tightly controlled, with the Guardian Council allowing just six people - and no women - to stand for election.

Among the three other candidates include two moderate reformists - Mostafa Hashemitaba and Vice-president Eshaq Jahangiri - and one hardliner, all of whom are not expected to win the presidency.

The selection of these candidates appears to be an attempt to balance moderates and hardliners in the upcoming debates, AFP reported.

Candidates must win over 50 percent of the vote to be guaranteed the position, otherwise another round of voting takes places between the top two hopefuls.